Novel insights into safety and quality enhancement of low-salt fermented chilies: High-order positively interacting lactic acid bacteria co-fermentation regulates microflora structure, metabolomics, and volatilomics profiles

Microbial interactions, with their impact on community structure and function, emerge as a promising strategy for regulating low-salt fermented foods' safety and quality. Here, the mechanisms of microbial interaction on the safety and quality improvement of low-salt fermented chilies (LSFC) were untangled through high-throughput sequencing, gas chromatography-mass spectrometry, interaction networks, co-fermentation, and multivariate statistical analyses. Results showed that 4 spoilage microorganisms (Acinetobacter, Cronobacter, Enterobacter, and Klebsiella), 139.96 mg/kg of biogenic amines, and 13 off-flavor compounds affected the safety and quality of lowsalt fermented chilies. Moreover, bacterial communities, mainly lactic acid bacteria (LAB) communities (relative abundance of 58.27-66.38%), were the primary contributors of volatile metabolites (diversity: R-2 = 0.60; structure: R-2 = 0.48; P < 0.001). Multiple interactions among LAB were quantified, including positive (11.7%), negative (55.0%), and neutral interactions (33.3%), in which positively interacting LAB community enhanced the robustness of in-situ community, resulting in the decrease of biogenic amines (decreased to 8.21 mg/kg) and the increase of the inhibition rate of Enterobacter hormaechei (inhibition rate of 80.31%). Additionally, cofermentation experiments showed that the higher-order positively interacting LAB community (Leu. mesenteroides, Lac. plantarum, and Lac. brevis) corrected the microecological imbalance of the LSFC, increasing the content of linalool, 2,3-butanediol, and ethyl phenylacetate, and decreasing spoilage bacteria abundance and off-flavor compound types by 53.25% and 61.54%, respectively. Overall, the compatibility and niche competition between positively interacting communities and in-situ communities affect the microbial structure and function in LSFC. These findings provide new insights into enhancing low-salt fermented foods' biochemical safety and flavor quality.